In wafer fabrication, the wafers pass many times in and out of four basic operations. Such are layering, patterning, doping, and heat processing. In final packaging of dies cut from wafers, there are also several basic operations. As in fabrication, the exact order of the operation is determined by the package type and other factors. However, in packaging the flow is linear, with the semiconductor dies proceeding from one operation to the next, only going through the individual packaging operations once. As a general matter, the packaging operations for semiconductor devices include backside preparation, die separation, die pick, inspection, die attach, wire bonding, pre-seal inspection, package sealing, plating, trim, marking, and final test.
There are four basic functions performed by a semiconductor package. They are to provide a lead system, physical protection, environmental protection, and heat dissipation. In this regard, the primary function of the package is to allow connection of the chip or semiconductor device to a circuit board or directly to an electronic product. The second function of the package is the physical protection of the semiconductor device from breakage, contamination and abuse. Physical protection needs vary from low, as in the case of consumer products, to very stringent, as is the case for electronic circuits used in automobiles, space vehicles, and military applications. Environmental protection, on the other hand, for semiconductor devices is to protect the semiconductor device from chemicals, moisture and gases that may interfere with its functioning. Still further, every semiconductor device generates heat during operation. The package enclosure materials used with semiconductor devices serve in nearly all instances, to draw the heat away from the enclosed semiconductor devices thereby dissipating same.
One method of providing an enclosure includes the use of a two part epoxy system. Such is typically very slow to cure, with the epoxy remaining in a flowable state while it cures. Curing times for such epoxy materials may take 24 hours or more. Due in part to the flowable nature of the epoxy, such packaging requires that the semiconductor devices be maintained in a precisely level state for a significant period of time as the epoxy cures. This requirement, of course, reduces the throughput of this packaging method and is therefore very costly, and not conducive to high volume production.
A novel packaging method which addresses the shortcomings identified above, is the subject of the present invention.